There are a wide variety of voltage converters available today, one type being the buck converter. Generally, a buck converter receives an input voltage and provides a stepped-down output voltage with a stepped-up output current. In other words, buck converters may typically be used in applications where it is desired to decrease a Direct Current (DC) voltage. Example applications include processing cores, where a buck converter is used to step down a DC voltage from a voltage rail so that the output voltage of the buck converter corresponds to an appropriate input voltage of the processing core.
An example conventional buck converter includes multiple switches at an input of the buck converter. The switches are turned on and off by a pulse width modulated input signal, where the duty cycle of the pulses determines an output voltage of the buck converter. As the switches turn on and off, they modulate a DC input voltage (sometimes referred to as VDD) and provide that modulated voltage to an inductor. The inductor is in communication with a capacitor, and the time-varying nature of the voltage at the input of the inductor causes the inductor to create a time-varying current. The interaction of the inductor and capacitor with the time-varying voltage and current produces a substantially constant output voltage, which is at a lower DC level than VDD.
One variety of buck converter is a three-level buck converter. Conventional three-level buck converters enjoy an effective doubling of their switching frequency. In one example, a conventional three-level buck converter has four input switches that each receive one of two pulse width modulated input signals. The timing of the two pulse width modulated input signals and the arrangement of the switches provides for an input voltage at the inductor that is at twice a frequency of the pulse width modulated input signals. In this conventional example, the input voltage at the inductor may vary between zero and VDD/2 or between VDD/2 and VDD, depending on the duty cycle of the pulse width modulated signals.
Three-level buck converters may be advantageous in some applications because an effective doubling of the switching frequency may allow for use of a smaller inductor. However, conventional three-level buck converters may sometimes experience ripple at the node between the switches and the inductor. Ripple may be undesirable in some applications because it may result in an unwanted variation of the output voltage of the buck converter. Thus, there is a need for improved three-level buck converters that reduce the ripple currents.